Duplex coating for thermal and corrosion protection

Method for producing a duplex coating on a substrate to impart thermal and corrosion resistance thereto comprising:

• a. plasma depositing on said substrate as a primary layer a first sublayer wherein the particle size of the powder is less than 44 microns and then depositing a second sublayer on said first sublayer wherein the particle size of the powder has a significant fraction greater than 44 microns using powder consisting of a metal alloy selected from the class consisting of nickel alloys, cobalt alloys, iron alloys and mixtures thereof with additions of at least one metal selected from the group consisting of 10 to 50 wt.% chromium, 5 to 25% aluminum, 0.5 to 10wt.% of another metal selected from the class consisting of yttrium, rare earth metals, hafnium, tantalum, tungsten, zirconium, platinum, rhodium, paladium, and silicon, and said layer having a surface roughness of at least 250 .times. 10.sup.-6 inches AA;
• b. plasma depositing an oxide layer on said rough primary layer surface such oxide layer consisting of an oxide taken from the class consisting of zirconia, stabilized zirconia, magnesium zirconate and alumina and having a density of less than 88%;
• c. and heat treating said duplex coating in a non-oxidizing atmosphere at a time and temperature to permit sintering of the components of the primary layer to cause effective sealing of the primary layer.